“A thick lump of dust, rocks, and gas” is how astronomer Jane Greaves of the University of St. Andrews in Scotland describes the new protoplanet she reported on in April at a meeting in Belfast sponsored by the Royal Astronomical Society. The dusty, rocky, gaseous lump, circling a star 520 light-years from Earth, is the youngest planet-in-the-making ever found.

“Normally when people talk about stars with planets forming, they’re often talking about a system that’s a billion years old,” Greaves says. But she trained her search for forming planets on the baby star HL Tau, which is just 100,000 years old. Using an unusual configuration of radio telescopes to detect particles the size of pebbles, Greaves found a dense clump in the disk of gas and dust surrounding the star. Planets build from such clumps—or so it is believed. Now astronomers can monitor the nascent object designated HL Tau b to find out.

Computer models suggest a brush with a nearby star may have triggered the clumping as recently as 2,000 years ago. (Earth, in contrast, is more than 4.5 billion years old.) In another few hundred thousand years or so, Greaves predicts, the planet will have grown from an inchoate lump to a gas giant larger than any in our solar system, “a very beefed-up version of Jupiter.”